1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor light emitting device employing a Pd electrode.
2. Background Art
In semiconductor light emitting devices, the p-type semiconductor layer formed over the active layer is partially connected to the p-type electrode for receiving electrical power and delivering it to the p-type semiconductor layer. That portion of the p-type semiconductor layer connected to the p-type electrode is referred to as the “p-type contact layer.” In order to improve the characteristics of the device, e.g., reduce its current consumption, it is necessary that the p-type electrode have good ohmic characteristics and low contact resistance with respect to the underlying p-type contact layer.
For example, the p-type electrode material of some nitride semiconductor light emitting devices used as blue-violet LDs is Pd or contains Pd to meet the above requirement. The Pd electrode is formed at least on the p-type contact layer. However, it is common that the Pd electrode is also formed on an insulating film(s) (which is formed on the p-type semiconductor layer) in order to ensure sufficient process margin. That is, the Pd electrode usually consists of two portions, the contact covering portion and the insulating film covering portion. Further, a pad electrode is formed on the Pd electrode after the formation of the Pd electrode.
Prior art includes Japanese Laid-Open Patent Publication Nos. 60-43830 (1985), 2005-93673, 2003-100758, 2002-205268, 10-74710 (1998), 5-152248 (1993), 1-116070 (1989), 2006-351617, and 2006-245379.
However, since the Pd electrode has poor adhesion to the insulating film, the insulating film covering portion of the Pd electrode may peel off. Some of the material flaked off from the insulating film covering portion may adhere to the surface of the semiconductor light emitting device, thereby reducing the manufacturing yield. Further, in this connection, the insulating film covering portion of the Pd electrode may not completely peel off, but may overhang from the edges of the contact covering portion of the Pd electrode, which prevents the pad electrode from being formed in the desired place at the subsequent pad electrode forming step. This may result in the formation of voids or holes in the pad electrode. Further, the peeling off of the insulating film covering portion of the Pd electrode may result in the peeling off of part of the contact covering portion, exposing a surface of the p-type contact layer. This means that the pad electrode is formed directly on the exposed surface of the p-type contact layer. In such a case, Au, etc. contained in the pad electrode may diffuse into the p-type semiconductor layer, thereby degrading the characteristics and reliability of the semiconductor light emitting device.
In order to prevent the peeling of the insulating film covering portion of the Pd electrode, an adhesive layer may be additionally formed between the insulating film and the Pd electrode to enhance their adhesion to each other. However, forming the adhesive layer in the desired place requires an additional process step, resulting in increased manufacturing cost.